A co-generation system which supplies electric power and heat at the same time has been known. This co-generation system generates power by driving a gas turbine or the like with fuel gas such as city gas, and produces steam by heating a boiler with produced exhaust gas, thus being a heat-and-power supply system capable of achieving a high thermal efficiency in total. For instance, Patent Document 1 discloses a co-generation system which generates power with a gas turbine and supplies the generated power to a complex facility such as a department store, and utilizes thermal energy of exhaust gas as energy for air conditioning in the facility.